1. Field of the Invention
The present invention relates to a fixing apparatus favorably for use in an electrophotographic image forming apparatus, and to an image forming apparatus having the same.
2. Description of the Related Art
In an image formation using an electrophotographic system, a photoreceptor charged with a uniform electric potential is exposed to light in accordance with image information so that an electrostatic latent image is formed. The formed electrostatic latent image is developed by a developer so as to be visualized. The visualized image is transferred on a recording paper or the like, and the transferred developer on the recording paper is made to be fixed so as to form a solid recording image.
The fixing apparatus used for such image formation, is generally composed of a heating roller and a pressure roller. The fixing apparatus has such a configuration that, in passing the recording paper on which the developer for forming a visualized image through a press-contact region (hereinafter referred to as a nip portion) of the heating roller and the pressure roller, which press-contact region is formed by pressing the pressure roller against the heating roller, unfixed developer is fused and fixed by heating of the heating roller and pressing of the pressure roller.
During a fixing operation in the fixing apparatus, there sometimes occurs a so-called hot offset that the developer fused on the nip portion of the both rollers is not all fixed on the recording paper, but a part of the developer is attached to a surface of the roller. For instance, the developer attached to the heating roller is transferred on a portion which should be properly a white base, on a recording paper on which the developer is to be subsequently fixed, with the result that an image defect is made to occur.
Moreover, on the pressure roller, the developer which has already fixed to a back surface of the conveyed recording paper, for instance as in a case of duplex print, is sometimes fused again by heat in passing through the nip portion and a part of the developer is transferred and attached to the pressure roller. The developer thus attached to the pressure roller may cause the image defect and further, may cause a soil of the back surface of the recording paper.
The image defect caused by the hot offset in the fixing apparatus sometimes remains, in a case of black-and-white print, mere defects such as a fog in a white base of the formed image, a soil on the back surface of the recording paper, or the like in a tolerable range. However, in a case of full-color print, since a developer having a color different from a prescribed one is transferred from the both rollers, there often occur practically intolerable defects.
As a related art for solving such a problem, there is an apparatus having roller cleaning units on the both rollers provided in a fixing apparatus (refer to Japanese Unexamined Patent Publication JP-A 2003-107952).
FIG. 5 is a schematic view showing a configuration of a roller cleaning unit 1 provided in a related art fixing apparatus. FIG. 5 illustrates the roller cleaning unit 1 provided on a heating roller 2 in the fixing apparatus.
The roller cleaning unit 1 comprises a feeding roller 4 for feeding a belt-shaped cleaning member 3 which has been previously rolled up, a winding roller 5 for taking up the cleaning member 3 fed from the feeding roller 4, and a press-contact roller 6 (also referred to as a web press-contact roller) provided between the feeding roller 4 and the winding roller 5 so as to press the cleaning member 3 on the heating roller 2.
The roller cleaning unit 1 presses the cleaning member 3 on the heating roller 2 which is rotated in an arrow sign 7 direction in a state where the winding roller 5, the feeding roller 4, and the press-contact roller 6 are made to be at rest without being rotated so that the heating roller 2 and the cleaning member 3 are made to be slidingly scrubbed with each other. By so doing, a developer 8a attached in a fused state to an outer circumferential surface of the heating roller 2 is removed and the removed developer 8b is accumulated, still in a substantially fused state, in a gap formed by the cleaning member 3 located between the press-contact roller 6 and the winding roller 5, and the surface of the heating roller 2.
When the developer 8b accumulated in the gap reaches a certain amount, the roller cleaning unit 1 causes the wind-up roller 5 to perform a wind-up operation in a direction of an arrow 9 and wind up the cleaning member 3 by a predetermined length, thereby removing the developer 8b from the surface of the heating roller 2 with the developer adhered to the cleaning member 3.
The cleaning member 3 used to clean the roller in this way is impregnated with oil such as silicone oil in advance, for the purpose of increasing the releasability of residual toner, which is a residual developer adhering to a fixing roller, and increasing the heat resistance of the cleaning member 3 itself. That is to say, through sliding contact of the cleaning member 3 and, for example, the heating roller 2, the oil impregnated into the cleaning member 3 is applied to the surface of the heating roller 2, whereby the releasability of the toner adhering to the surface of the heating roller 2 is increased, and the heat resistance of the cleaning member 3 itself at a fixing temperature raised up to about 200° C. is increased.
However, since fixing rollers formed by the heating roller 2 and a pressure roller are heated and warmed in order to fix a toner image, the cleaning member 3 disposed so as to contact the fixing roller is warmed by heat transmitted from the fixing roller, and such a phenomenon is caused by warming that the impregnated oil seeps and flows out onto the fixing roller. FIG. 6 is a view illustrating a state where the oil has seeped out of the cleaning member 3. There is a problem that the oil flowing out onto the fixing roller (the heating roller 2 in FIG. 6) forms an oil puddle 10 on the fixing roller, and scatters in the apparatus as the fixing roller rotates or evaporates by being heated by the fixing roller to adhere to every part in the apparatus, thereby causing contamination. Moreover, there is a problem that the oil penetrates into a recording sheet, which is a medium for recording a toner image, passing through between the fixing rollers, and soils the recording sheet, thereby changing the gloss thereof.